Magnetic multilayer film and magnetoresistance element

ABSTRACT

A magnetic multilayer film having magnetoresistance (MR) is prepared by depositing at least two magnetic thin films having different coercive forces while interposing a non-magnetic thin film therebetween. A first magnetic thin film having a lower coercive force has a squareness ratio SQ 1  of 0.01-0.5, an anisotropic magnetic field Hk of 1-20 Oe, and a thickness t 1 , a second magnetic thin film having a higher coercive force has a squareness ratio SQ 2  of 0.7-1.0 and a thickness t 2  ≦t 1 , and the non-magnetic thin film has a thickness t 3  ≦200 Å. A first preferred form requires 4 Å≦t 2  &lt;30 Å and 6 Å≦t 1  ≦200 Å. A second preferred form requires 4 Å≦t 2  &lt;20 Å and 10 Å≦t 1  &lt;20 Å. A third preferred form requires 4 Å≦t 2  &lt;30 Å and 6 Å≦t 1  ≦40 Å. The magnetic multilayer film has a great MR ratio of more than several percents in a low external magnetic field, a sharp rise at zero magnetic field and high heat resistance. It also has improved hysteresis and MR slope in an applied magnetic field between -10 Oe and +10 Oe. It additionally has a high MR slope of at least 0.15%/Oe in an applied magnetic field between -50 Oe and +50 Oe, improved hysteresis of MR ratio, and a high MR slope in a high-frequency magnetic field. There are obtained high sensitivity MR sensors and MR heads capable of high density magnetic recording.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a magnetoresistance element for reading themagnetic field intensity of magnetic recording media as signals,especially a magnetoresistance element capable of reading a smallmagnetic field change as a greater electrical resistance change signaland a magnetic multilayer film suitable for use therein. The term"magnetoresistance" is often abbreviated as MR, hereinafter.

2. Prior Art

There are growing demands for increasing the sensitivity of magneticsensors and increasing the density of magnetic recording. Activeresearch works have been devoted for the development ofmagnetoresistance effect type magnetic sensors (simply referred to as MRsensors, hereinafter) and magnetoresistance effect type magnetic heads(simply referred to as MR heads, hereinafter). Both MR sensors and MRheads are designed to read out external magnetic field signals bydetecting changes in the resistance of a reading sensors portion formedof magnetic material. The MR sensors have the advantage of highsensitivity and the MR heads have the advantage of high outputs in highdensity magnetic recording since the reproduced output does not dependon the relative speed of the sensors or heads to the recording medium.

Conventional MR sensors of magnetic materials such as Ni₀.8 Fe₀.2(Permalloy) and NiCo utilizing anisotropic magnetoresistance effectoffer only an MR ratio ΔR/R as small as 2 to 5% and are low insensitivity as reading MR beads adapted to accommodate for ultrahighdensity recording of the order of several GBPI.

Attention is now paid to artificial superlattices having the structurein which thin films of metal having a thickness of an atomic diameterorder are periodically stacked since their behavior is different frombulk metal. One of such artificial superlattices is a magneticmultilayer film having ferromagnetic metal thin films andantiferromagnetic metal thin films alternately deposited on a substrate.Heretofore known are magnetic multilayer films of iron-chromium andcobalt-copper types. Among them, the iron-chromium (Fe/Cr) type wasreported to exhibit a magnetoresistance change in excess of 40% atliquid He temperature (4.2K) (see Phys. Rev. Lett., Vol. 61, page 2472,1988). This artificial superlattice magnetic multilayer film, however,is not commercially applicable as such because the external magneticfield at which a maximum resistance change occurs (that is, operatingmagnetic field intensity) is as high as ten to several tens ofkilooersted (kOe). Additionally, there have been proposed artificialsuperlattice magnetic multilayer films of Co/Ag, which require too highoperating magnetic field intensity.

Under these circumstances, a three-element or ternary magneticmultilayer film having two magnetic layers having different coerciveforces deposited through a non-magnetic layer was proposed as exhibitinga giant MR change due to induced ferrimagnetism. For example, EuropeanPatent Application No. 0483 373 proposing such a magnetic multilayerfilm in which two magnetic layers disposed adjacent to each otherthrough a non-magnetic layer have different coercive forces (Hc) and athickness of up to 200 Å. Also the following reports are known.

(a) T. Shinjo and H. Yamamoto, Journal of the Physical Society of Japan,Vol. 59 (1990), page 3061

Co(30)/Cu(50)/NiFe(30)/Cu(50)!x15 wherein the number in the parenthesesrepresents the thickness in angstrom of the associated layer and thenumber after "x" is the number of repetition (the same applieshereinafter) produced an MR ratio of 9.9% at an applied magnetic fieldof 3000 Oe and about 8.5% at 500 Oe.

(b) H. Yamamoto, Y. Okuyama, H. Dohnomae and T. Shinjo, Journal ofMagnetism and Magnetic Materials, Vol. 99 (1991), page 243

In addition to (a), this article discusses the results of structuralanalysis, changes with temperature of MR ratio and resistivity, changeswith the angle of external magnetic field, a minor loop of MR curve,dependency on stacking number, dependency on Cu layer thickness, andchanges of magnetization curve.

(c) Hoshino, Hosoe, Jinpo, Kanda, Tsunashima and Uchiyama, Proceedingsof Magnetics Research Meeting of the Japanese Electrical Society,MAG-91-161

This is a confirmation test of (a) and (b). Included are test ofdependency on Cu layer thickness and dependency on NiFe layer thickness.Also reported is the result about the dependency of coercivity of Co onCu layer thickness which is simulatively determined from themagnetization curve by extrapolation. Magnetization curves are derivedfrom NiFe(30)-Cu(320) and Co(30)-Cu(320) and synthesized for comparisonwith a magnetization curve of NiFe(30)-Cu(160)-Co(30)-Cu(160). Since thethickness of the Cu intermediate layer is different from that of athree-element multilayer, direct comparison of squareness ratio andcoercivity is impossible.

(d) Okuyama, Yamamoto and Shinjo, Proceedings of Magnetics ResearchMeeting of the Japanese Electrical Society, MAG-91-242

This article describes the phenomenological analysis on giant MR changesby induced ferrimagnetism. With the rotation of magnetic moment of anNiFe layer with low Hc, MR similarly changes. A giant MR phenomenondevelops due to the artificially created spin anti-parallelism. It isproven by a difference in MR by an angular change of the appliedmagnetic field that this phenomenon is different from the anisotropic MReffect of NiFe or the like.

(e) H. Sakakima et al., Japanese Journal of Applied Physics, 31 (1992),L484

For RF sputtered NiFe/Co/Cu/Co multilayer film, micro-structure and MRratio are examined. Reported is an oscillatory phenomenon of MR ratiowith the thickness of Cu layer when both the NiFe and Co layers have afixed thickness of 30 Å. No magnetic field is applied during layerdeposition.

(f) EP-A1 0483 373/1991

Disclosed is a magnetic multilayer film having two magnetic layershaving different coercive forces stacked through an interveningnon-magnetic layer. An exemplary structure includes a Ni-Fe layer of 25Å or 30 Å thick, an intervening Cu layer, and a Co layer of 25 Å or 30 Åthick.

(g) JP-A 223306/1992

Disclosed is a magnetic multilayer film having two magnetic layershaving different coercive forces stacked through an interveningnon-magnetic layer. One magnetic layer is of CoPt base material.

These three-element magnetic multilayer films exhibit a giant MR ratioof about 10% under an applied magnetic field of up to about severalhundreds of coersted, though the magnitude of MR ratio is small ascompared with Fe/Cr, Co/Cu and Co/Ag. It is to be noted that thesedisclosures refer to only MR changes under an applied magnetic field ofup to about 10 to 100 Oe.

For practical MR head material to find use in ultra-high densitymagnetic recording, an MR curve under an applied magnetic field of 0 toabout 40 or 50 Oe is critical. The above-mentioned prior artthree-element artificial superlattices, however, failed to increase MRchanges under zero magnetic field, with an MR changes approximate to 0.An increase of MR change becomes maximum at about 60 Oe and an MR ratioof about 9% is then obtained. This implies that the MR curve has a slowrise. In the case of Permalloy (NiFe), the MR change has a gradient ofapproximately 0 across zero magnetic field, the MR ratio remainssubstantially unchanged, the differential value of MR ratio is close to0, and magnetic field sensitivity is low. The material is not suitableas reading MR heads for ultra-high density magnetic recording.

For overcoming such properties, NiFe is provided with a shunt layerhaving low resistivity such as Ti for providing a shift of the operatingpoint. In addition to the shunt layer, a soft film bias layer of softmagnetic material having a high resistivity such as CoZrMo and NiFeRh isprovided for applying a bias magnetic field. The structure having such abias layer, however, is complex in steps, difficult to provide stableproperties, and increased in cost. It also invites a lowering of S/Nsince it uses a relatively moderate portion of the MR curve.

Moreover, MR heads have a complex layered structure, require heattreatment such as baking and curing of resist material during patterningand flattening steps, and must tolerate temperatures of about 350° C.Conventional three-element artificial superlattice magnetic multilayerfilms, however, degrade their properties during such heat treatment.

The following reports were published after the filing date in Japan ofthe basic application, but before the filing date of this application inthe U.S.

(h) EP-A1 0498 344/1992

Disclosed is a magnetic multilayer film having stacked through anintervening non-magnetic thin film two magnetic thin films of (Ni_(x)Co_(1-x))_(x') Fe_(1-x') and (Co_(y) Ni_(1-y))_(z) Fe_(1-z) whereinx=0.6-1.0, x'=0.7-1.0, y=0.4-1.0, and z=0.8-1.0. An exemplary structureincludes a non-magnetic thin film of 50 Å thick intervening between twomagnetic thin films of 30 Å thick.

(i) T. Valet et al., Applied Physics Letters, 61 (1992) 3187

For RF sputtered Ni₈₀ Fe₂₀ /Cu/Co multilayer film, an oscillatoryphenomenon of MR ratio with the thickness of Cu layer is reported.Samples of NiFe(50)-Cu(x)-Co(20)-Cu(x)!x3 wherein 7≦x≦37 were deposed byRF sputtering in the absence of a magnetic field. It is described thatan MR change component attributable to differential coercive force isfound only at x=33 Å.

(j) T. Valet et al., Journal of Magnetism and Magnetic Materials, 121(1993) 402

For RF sputtered Ni₈₀ Fe₂₀ /Cu/Co multilayer film, micro-structure andMR change are examined. Reported are cross-sectional electronphotomicrographs (TEM) of two samples: NiFe(50)-Cu(50)-Co(10)-Cu(50)!x12and NiFe(50)-Cu(50)-Co(100)-Cu(50)!x8, and MR characteristics of twosamples: NiFe(50)-Cu(20)-Co(30)-Cu(20)!x18 andNiFe(50)-Cu(20)-Co(30)-Cu(20)!x3. A 18-layer stack, for example, showsan MR change of 11% at room temperature which is allegedly attributableto differential coercive force. No magnetic field is applied duringlayer deposition.

(k) Journal of Magnetism and Magnetic Materials, 121 (1993) 339

Described is a magnetization reversal mechanism of sputteredNiFe(50)-Cu(x)-Co(20)-Cu(x)!x3. MR characteristics are referred tonowhere. No magnetic field is applied during layer deposition.

In the aforementioned publications, no magnetic field is applied duringlayer deposition and NiFe layers are provided with no magneticanisotropy and thus have high squareness ratios. As a result, the MRratio in the range between -10 Oe and +10 Oe has great hysteresiscentered at zero magnetic field and the MR slope in that range is small,indicating failure to provide satisfactory and stable reproduction asmagnetic heads.

For MR heads intended for ultra-high density magnetic recording, an MRchange curve under an applied magnetic field between -50 Oe and +50 Oeis important. However, in all the examples of the aforementionedpublications, the MR ratio in the range between -50 Oe and +50 Oe hasgreat hysteresis centered at zero magnetic field and the MR slope inthat range is small.

Often MR heads are used in a high-frequency magnetic field of 1 MHz orhigher for reproduction of high density recorded signals. Most prior artthree-element magnetic multilayer films are difficult to provide highhigh-frequency sensitivity by producing an MR slope (or MR change curveslope) of 0.08%/Oe or more in a high-frequency magnetic field of 1 MHzor higher partly because of their film thickness combination.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a novel andimproved magnetic multilayer film exhibiting a high MR ratio, a linearrise of MR change under an applied magnetic field of a narrow range, forexample, of 0 to 40 Oe, high magnetic field sensitivity, and high heatresistant temperature.

Another object of the present invention is to provide a novel andimproved magnetic multilayer film which is improved in hysteresis and MRslope under an applied magnetic field, for example, between -10 Oe and+10 Oe.

A further object of the present invention is to provide a novel andimproved magnetic multilayer film which exhibits a great MR slope of atleast 0.15%/Oe under an applied magnetic field, for example, in therange between -50 Oe and +50 Oe, improved hysteresis, and a great MRslope under a high-frequency magnetic field.

A still further object is to provide a magnetoresistance element usingsuch a magnetic multilayer film.

According to the present invention, a magnetic multilayer film includesat least two magnetic thin films stacked through an interveningnon-magnetic thin film. The magnetic thin films adjoin each otherthrough the non-magnetic thin film and have different coercive forces. Afirst magnetic thin film having a lower coercive force has a thicknesst₁ and a squareness ratio SQ₁ of 0.01 to 0.5, a second magnetic thinfilm having a higher coercive force has a thickness t₂ and a squarenessratio SQ₂ of 0.7 to 1.0, and the non-magnetic thin film has a thicknesst₃. All the thicknesses t₁, t₂ and t₃ are up to 200 Å.

Preferably SQ₂ /SQ₁ ranges from 2 to 100. The first magnetic thin filmhas an anisotropic magnetic field Hk of 1 to 20 Oe, more preferably 3 to20 Oe.

In a first preferred form of the present invention, the film thicknessest₁, t₂ and t₃ are controlled to fall in the range: 4 Å≦t₂ <30 Å, 6 Å≦t₁≦200 Å, t₁ ≧t₂, and t₃ ≦200 Å. In a second preferred form of the presentinvention, the film thicknesses t₁, t₂ and t₃ are controlled to fall inthe range: 4 Å≦t₂ <20 Å, 10 Å≦t₁ <20 Å, t₁ ≧t₂, and t₃ ≦200 Å. In athird preferred form of the present invention, the film thicknesses t₁,t₂ and t₃ are controlled to fall in the range: 4 Å≦t₂ <30 Å, 6 Å≦t₁ ≦40Å, t₁ ≧t₂, and more preferably t₃ <50 Å.

Preferably, the magnetic multilayer film produces a magnetoresistancecurve including a linear portion having a slope of at least 0.15%/Oe inthe magnetic field range between -50 Oe and +50 Oe. The curve has amaximum hysteresis width of up to 20 Oe.

Preferably, the first magnetic thin film has a composition (Ni_(x)Fe_(1-x))_(y) Co_(1-y) wherein 0.7≦x≦0.9 and 0.5≦y≦1.0. The secondmagnetic thin film has a composition (Co_(z) Ni_(1-z))_(w) Fe_(1-w)wherein 0.4≦z≦1.0 and 0.5≦w≦1.0.

A magnetic multilayer film as defined above is preferably prepared by amethod including applying a magnetic field of 10 to 300 Oe in onein-plane direction during deposition of the first magnetic thin film.The method further includes depositing at least two magnetic thin films,while interposing a non-magnetic thin film therebetween and effectingheat treatment at a temperature of up to 500° C.

There is also provided a magnetoresistance element comprising a magneticmultilayer film as defined above on a substrate. The magnetoresistanceelement is free of a bias magnetic field applying mechanism.

ADVANTAGES

In order that a three-element magnetic multilayer film possess an MRcurve having good linearity across zero magnetic field and a steep slopeand improved heat resistance, only a difference in coercive force (Hc)as described in the above-cited references (a) to (d) is insufficient.The squareness ratio and thickness of first and second magnetic thinfilms must be restricted in accordance with the invention before such afavorable rise and heat resistance can be established. The squarenessratio and relative thickness of first and second magnetic thin films arenot taught in the above-cited publications (a) to (g) and our precedingapplication.

Where the magnetic thin films are thinner, there generates reducedmagnetic interaction between the first and second magnetic thin films sothat the multilayer film exhibits improved hysteresis and slope of MRratio under an applied magnetic field, for example, between -10 Oe and+10 Oe. This tendency is not taught in the above-cited publications.

In order that a three-element magnetic multilayer film show an MR slopeof at least 0.15%/Oe, which is a maximum differential value determinedfrom a differential curve of an MR curve developed under an appliedmagnetic field, for example, in the range between -50 Oe and +50 Oe,improved hysteresis, and a great MR slope under a high-frequencymagnetic field, the film thicknesses t₁, t₂ and t₃ are controlled tofall in the range defined in the third preferred form and the firstmagnetic thin film is deposed under an applied magnetic field. Suchrelative film thickness control and film formation under an appliedmagnetic field are not taught in the above-cited publications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmental cross section of a magnetic multilayer filmaccording to the invention.

FIG. 2 is a diagram showing exemplary B-H curves for explaining theprinciple of the invention.

FIG. 3 is a schematic view of a magnetoresistance element according toone embodiment of the invention.

FIG. 4 is a schematic view of a magnetoresistance element according toanother embodiment of the invention.

FIG. 5 is a cross sectional view of a magnetoresistance elementaccording to the invention as applied to a yoke type MR head.

FIG. 6 is diagrams showing M-H curves of first and second magnetic thinfilms as-deposited according to the first preferred form of theinvention.

FIG. 7 is a graph showing the slope at zero magnetic field of an MRcurve of a magnetic multilayer film in the first preferred form relativeto the Hk of the first magnetic thin film.

FIG. 8 is an X-ray diffraction pattern of a magnetic multilayer film inthe first preferred form as-deposited.

FIG. 9 is an X-ray diffraction pattern of a magnetic multilayer film inthe first preferred form after heat treatment.

FIG. 10 is a diagram showing MR ratio and applied magnetic field when amagnetic field in the range between -10 Oe and +10 Oe is applied to amagnetic multilayer film in the second preferred form.

FIG. 11 is a diagram showing the MR ratio of a magnetic multilayer filmin the third preferred form relative to the thickness of a Cu layer.

FIG. 12 is a diagram showing the maximum hysteresis width of an MR curveof a magnetic multilayer film in the third preferred form relative tothe thickness of a NiFe layer.

FIG. 13 is a diagram showing MR ratio and applied magnetic field when amagnetic field in the range between -50 Oe and +50 Oe is applied to amagnetic multilayer film in the third preferred form.

FIG. 14 is a diagram showing the MR slopes of a magnetic multilayer filmin the third preferred form and a comparative example relative to theheat treatment temperature.

FIG. 15 show X-ray diffraction patterns of magnetic multilayer films inthe third preferred form heat treated at different temperatures.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, first and second magnetic thin filmswhich are disposed adjacent to each other through a non-magnetic thinfilm must have different coercive forces. This is because the principleof the invention is that conducting electrons are subject tospin-dependent scattering to increase resistance as adjacent magneticlayers are offset in the direction of magnetization, and the resistancereaches maximum when the adjacent magnetic layers have oppositedirections of magnetization. More particularly, when an externalmagnetic field is intermediate the coercive force HC₁ of the firstmagnetic thin film and the coercive force HC₂ of the second magneticthin film (Hc₁ <H<Hc₂) as shown in FIG. 2, the adjacent magnetic layerswill have opposite components in their magnetization direction,resulting in an increased resistance.

Now, the external magnetic field, coercive force and magnetizationdirection of a three-element artificial superlattice magnetic multilayerfilm are described.

Referring to FIG. 1, there is shown in cross section an artificialsuperlattice magnetic multilayer film 1 according to one embodiment ofthe invention. The magnetic multilayer film 1 includes magnetic thinfilms M₁, M₂, . . . , M_(n-1), and M_(n) on a substrate 4 andnon-magnetic thin films N₁, N₂, . . . , N_(n-2), and N_(n-1) eachbetween a pair of two adjacent magnetic thin films.

For the sake of brevity of description only, reference is made to theembodiment having only two types of magnetic thin films having differentcoercive forces. As shown in FIG. 2, the two types of magnetic thinfilms (1) and (2) have different coercive forces Hc₁ and Hc₂,respectively (0<Hc₁ <Hc₂). The first magnetic thin film (1) has ananisotropic magnetic field Hk and the magnetization of the secondmagnetic thin film (2) is saturated at an external magnetic field Hm. Atthe initial, an external magnetic field H is applied wherein H<-Hm. Thefirst and second magnetic thin films (1) and (2) have magnetizationdirections oriented in a negative (-) direction same as H. Then theexternal magnetic field is increased to region I of H<-Hk where both themagnetic thin films have magnetization directions oriented in onedirection. As the external magnetic field is increased to region II of-Hk<H<Hk, magnetic thin film (1) partially starts reversing itsmagnetization direction so that the magnetization directions of magneticthin films (1) and (2) may include opposite components. Themagnetization directions of magnetic thin films (1) and (2) areinsubstantially complete anti-parallelism in the range of Hk<H<Hc₂. Whenthe external magnetic field is further increased to region III of Hm<H,magnetic thin films (1) and (2) have magnetization directions aligned ina positive (+) direction.

Now, the external magnetic field H is reduced. In region IV of Hk<H, themagnetic thin films (1) and (2) have magnetization directions stillaligned in as positive (+) direction. In region V of -Hk<H<+Hk, themagnetic thin film (1) starts reversing its magnetization direction inone direction so that the magnetization directions of magnetic thinfilms (1) and (2) may include opposite components. Subsequently inregion VI of H<-Hm, the magnetic thin films (1) and (2) havemagnetization directions aligned in one direction again.

In the regions II and V where the magnetic thin films (1) and (2) haveopposite magnetization directions, conducting electrons are subject tospin-dependent scattering, resulting in an increased resistance. In thezone of -Hk<H<Hk in region II, magnetic thin film (2) undergoes littlemagnetization reversal, but magnetic thin film (1) linearly increasesits magnetization, the proportion of conducting electrons subject tospin-dependent scattering is gradually increased in accordance with amagnetization change of magnetic thin film (1). By selecting a low Hcmaterial such as Ni₀.8 Fe₀.2 (Hc₂ =several Oe) as the first magneticthin film (1), imparting appropriate Hk thereto and selecting a somewhathigh Hc, high squareness ratio material such as Co (Hc₂ =several tens ofOe) as the second magnetic thin film (2), for example, there is obtainedan MR element exhibiting a linear MR change and a great MR ratio in alow external magnetic field in the range of several oersteds to severaltens of oersted near or below Hk.

The magnetic materials of which the magnetic thin films are formedherein are not critical although they are preferably selected from Fe,Ni, Co, Mn, Cr, Dy, Er, Nd, Tb, Tm, Ce and Gd. Also useful are alloysand compounds containing these elements, for example, Fe--Si, Fe--Ni,Fe--Co, Fe--Al, Fe--Al--Si (Sendust, etc.), Fe--Y, Fe--Gd, Fe--Mn,Co--Ni, Cr--Sb, Fe system amorphous alloys, Co system amorphous alloys,Co--Pt, Fe--C, Mn--Sb, Ni--Mn, Co--O, Ni--O, Fe--O, Fe--Al--Si--N,Ni--F, and ferrite. In the practice of the invention, two or morematerials having different coercive forces are selected from theforegoing materials to form the magnetic thin films.

In the invention, the magnetic thin films have a thickness of up to 200Å. If the thickness exceeds 200 Å, the advantages are not lost, but nofurther advantages are obtained with a thickness increase, and wastesare increased upon manufacture. The lower limit of the magnetic thinfilm thickness is 4 Å below which the films have a Curie point lowerthan room temperature and lose practical value. A thickness of 4 Å ormore facilitates to form a film of uniform thickness and of quality andavoids an excess reduction of the magnitude of saturation magnetization.

In the invention, the respective magnetic thin films have coerciveforces Hc which may be suitably selected in the range of, for example,0.001 Oe to 10 kOe, especially 0.01 to 1000 Oe, depending on theintensity of an applied external magnetic field and the MR ratiorequired for the element associated therewith. The ratio in coerciveforce between adjacent magnetic thin films, Hc₂ /Hc₁ is preferably from1.2:1 to 100:1, especially from 1.5:1 to 100:1, more preferably from 2:1to 80:1, especially from 3:1 to 60:1, most preferably from 5:1 to 50:1,especially from 6:1 to 30:1. Outside the range, a higher ratio wouldresult in a broader MR curve whereas a lower ratio leads to a closedifference between coercive forces, failing to take advantage ofanti-parallelism.

Coercive force Hc is measured as follows because it is impossible todirectly measure the magnetic properties of magnetic thin films in amagnetoresistance element. Magnetic thin films to be measured for Hc aredeposited by evaporation alternately with non-magnetic thin films untilthe total thickness of the magnetic thin films reaches about 200 to 400Å. The resulting sample is measured for magnetic properties. It is to benoted that the thickness of magnetic thin films, the thickness ofnon-magnetic thin films, and the composition of non-magnetic thin filmsare the same as in a magnetoresistance element to be examined.

In order to provide an MR curve having good linearity across zeromagnetic field and improved heat resistance, the first magnetic thinfilm having lower Hc and the second magnetic thin film having higher Hcmust have controlled residual magnetization Mr at zero magnetic field,that is, controlled squareness ratio SQ=Mr/Ms. The first magnetic thinfilm should preferably have a squareness ratio SQ₁ of 0.01≦SQ₁ ≦0.5,more preferably 0.01≦SQ₁ ≦0.4, most preferably 0.01≦SQ₁ ≦0.3. The secondmagnetic thin film should preferably have a squareness ratio SQ₂ of0.7≦SQ₂ ≦1.0. Since the first magnetic thin film governs the rise of MRchange in the vicinity of zero magnetic field, its squareness ratio SQ₁as small as possible is preferred. More particularly, with smaller SQ1,magnetization will gradually rotate and anti-parallelism will graduallyincrease in the vicinity of zero magnetic field, resulting in a linearMR curve across zero magnetic field. With SQ₁ larger than 0.5, it isdifficult to provide a linear MR change. The lower limit of SQ₁ from themanufacturing aspect is about 0.01.

The second magnetic thin film to be combined with the first magneticthin film should preferably have a squareness ratio SQ₂ close to 1 inthe vicinity of zero magnetic field. With a squareness ratio SQ₂ of 0.7or higher, the rise of MR change in the vicinity of zero magnetic fieldbecomes sharp and a great MR ratio is obtainable. The first magneticthin film should preferably have an anisotropic magnetic field Hk of 1to 20 Oe, more preferably 2 to 12 Oe, most preferably 3 to 10 Oe. WithHk>20 Oe, the range of magnetic field where linearity is obtained isexpanded, but the slope of an MR curve is reduced with an accompanyingdrop of resolution. With Hk<1 Oe, linearity is obtained only in a rangeof magnetic field which is too narrow to exert the function as MRelements.

Preferably SQ₂ /SQ₁ is between 2 and 100, especially between 2 and 50.

It is desirable to more positively control the squareness ratio or therise of an MR curve and heat resistance by optimizing the thickness ofthe first and second magnetic thin films. If both the first and secondmagnetic thin films have an equal thickness as in most examplesdescribed in the above-cited publications (a) to (d), then both the thinfilms have a squareness ratio closer to 1.0 as their thicknessincreases. This means that the magnetization curve contains no definitebend of magnetization. As a result, the MR curve starts rising atseveral tens of Oe, undesirably exhibiting poor linearity at zeromagnetic field. Then the first and second magnetic thin films willexhibit better linearity or better rise when both are thin. However, ifboth are as thin as about 10 Å, for example, then a heat resistanceproblem arises. More particularly, when heated in vacuum at temperaturesof about 350° C., the first magnetic thin film undergoes a substantialloss of squareness ratio while the second magnetic thin film undergoeslittle loss of squareness ratio. It is found that the first magneticthin film will have a squareness ratio of up to 0.5 when it is thicker.Then by somewhat increasing the thickness of the first magnetic thinfilm independent of the second magnetic thin film, better MR propertiesare available after heat treatment. Heat resistance is improved whilesuppressing any deterioration of the squareness ratio of the firstmagnetic thin film after heat treatment.

Therefore, in addition to the limitation of SQ₁ and SQ₂, the thicknessest₁ and t₂ of the first and second magnetic thin films are preferablycontrolled to the range: 4 Å≦t₂ <30 Å, 6 Å≦t₁ ≦200 Å, and t₂ ≦t₁, morepreferably 4 Å≦t₂ ≦30 Å, 6 Å≦t₁ ≦200 Å, and t₂ ≦t₁.

In a first preferred form of the invention, these thicknesses arecontrolled to the range: 4 Å≦t₂ <30 Å, 20 Å≦t₁ ≦200 Å, and t₂ ≦t₁,preferably 4 Å≦t₂ ≦28 Å, 22 Å≦t₁ ≦100 Å, and t₂ <t₁, especially 1.05t₂≦t₁. With t₂ ≧30 Å, there is some likelihood that the overall structurehave increased resistivity and eventually a reduced MR ratio. It isimpossible to form a continuous film having a thickness t₂ <4 Å. With t₁<20 Å, there is some loss of heat resistance. For linearity, the upperlimit of t₁ is desirably 200 Å, especially 100 Å. If t₂ >t₁, thereresult low heat resistance and a reduced MR ratio when the structure issubject to heat during the manufacturing process.

By controlling the squareness ratio and thickness of the first andsecond magnetic thin films, a magnetic multilayer film as depositedexhibits an MR ratio as high as 5% or more, especially 60 to 12%, betterlinearity across zero magnetic field, and an increased MR slope. Morespecifically, the difference in MR ratio under an applied magnetic fieldof from -3 Oe to +3 Oe is 0.5% or more, typically about 1 to 2%, whichis sufficient as reading MR heads for ultra-high density recording.

By controlling t₁ and t₂ as mentioned above, the present inventionimproves heat resistance so that deterioration of properties, especiallyan MR ratio by heat treatment is minimized. More specifically, afterheat treatment in vacuum at 250° C. to about 350° C., for example, theMR ratio is maintained at 70% or more of that prior to heat treatment,that is, an MR ratio of at least 5%, especially at least 6% is obtained.Such heat treatment is encountered, for example, during an MR heatmanufacturing process. If a proper set of conditions is selected, thegradient across zero magnetic field as represented by the difference inMR ratio under an applied magnetic field between -3 Oe and +3 Oe will berather improved, for example, from 25% decrease prior to heat treatmentto 100% increase after heat treatment. A gradient of 0.5% or more,typically about 1 to 2%, which is sufficient as reading MR heads forultra-high density recording can be obtained even after heat treatment.It is to be noted that after heat treatment, SQ₁ remains in the range of0.01 to 0.5 and SQ₂ remains in the range of 0.7 to 1.0.

The non-magnetic thin films are formed of a material which plays therole of attenuating the magnetic interactions between magnetic thinfilms having different coercive forces. The non-magnetic material is notcritical and may be selected from metallic and metalloid non-magneticmaterials and non-metallic non-magnetic materials. Preferred examples ofthe metallic non-magnetic material include Au, Ag, Cu, Pt, Al, Mg, Mo,Zn, Nb, Ta, V, Hf, Sb, Zr, Ga, Ti, Sn and Pb and alloys thereof.Examples of the metalloid non-magnetic material include Si, Ge, C, andB, which may optionally contain an additional element or elements.Examples of the non-metallic non-magnetic material include SiO₂, SiO,SiN, Al₂ O₃, ZnO, MgO, and TiN, which may optionally contain anadditional element or elements.

In the first preferred form of the invention, the non-magnetic thin filmshould have a thickness t₃ of up to 200 Å. In general, with a filmthickness in excess of 200 Å, the resistance largely depends on anon-magnetic thin film, leaving little margin for spin-dependentscattering and resulting in a reduced MR ratio. On the other hand, anon-magnetic thin film of a reduced thickness will allow greatermagnetic interactions to develop between magnetic thin films,prohibiting both the magnetic thin films from exhibiting differentmagnetization directions, and it is difficult to form a continuous filmof such a reduced thickness. For these reasons, a thickness of at least4 Å is preferred. The more preferred range of t₃ is less than 50 Å aswill be described later.

Understandably, the thickness of magnetic thin films and non-magneticthin films can be measured by means of a transmission electronmicroscope or scanning electron microscope or by Auger electronspectroscopy. The crystal structure of thin films can be observed byX-ray diffraction or high speed electron diffraction analysis.

The second preferred form of the invention requires to control therespective film thicknesses to fall in the range: 4 Å≦t₂ <20 Å, 10 Å≦t₁<20 Å, t₁ ≧t₂. By reducing the thicknesses of the magnetic thin films,the magnetic interactions between the first and second magnetic thinfilms via the non-magnetic thin film layer are reduced so that therespective magnetic thin films can be independently liable tomagnetization reversal. Then the multilayer film exhibits a high MRratio as well as excellent hysteresis properties of MR ratio and a sharpMR slope in an applied magnetic field, for example, in the range between-10 Oe and +10 Oe. It is impossible to form a continuous film having athickness t₂ <4 Å. If t₂ >t₁, the ratio between the overallmagnetization quantities of the first and second magnetic thin filmlayers goes out of balance and the proportion of conducting electronssubject to spin-dependent scattering is reduced, resulting in losses ofproperties.

Even when the thicknesses of the magnetic thin films are reduced asdefined above, heat resistance at about 250° C. remains high enough forpractical applications. With respect to the magnetic materials, coerciveforce Hc, squareness ratio SQ₂ /SQ₁ and anisotropic magnetic field Hk ofthe magnetic thin films, and the non-magnetic thin film, the sameconditions as previously described are useful.

In the third preferred form of the invention, the thicknesses t₁, t₂ andt₃ of the first magnetic thin film, second magnetic thin film andnon-magnetic thin film should be controlled to fall in the range: 4 Å≦t₂<30 Å, 6 Å≦t₁ ≦40 Å, t₁ ≧t₂, and t₃ <50 Å, more preferably 6 Å≦t₂ ≦28 Å,8 Å≦t₁ ≦36 Å, t₁ >t₂, especially t₁ ≧1.05t₂, and 8 Å≦t₃ ≦48 Å. With t₂≧30 Å, there is some likelihood that the overall structure haveincreased resistivity and eventually a reduced MR ratio. It isimpossible to form a continuous film having a thickness t₂ <4 Å. Witht₁ >40 Å, the maximum hysteresis width of an MR curve exceeds 20 Oe, andif the resulting MR element is used as a magnetic head, thereundesirably appears a widely varying output voltage. With t₁ <6 Å, thestructure would show unsatisfactory magnetic properties, resulting inlosses of MR ratio, MR slope and heat resistance, and its MR curve wouldhave an increased maximum hysteresis width. If t₂ >t₁, the ratio betweenthe overall magnetization quantities of the first and second magneticthin film layers goes out of balance and the proportion of conductingelectrons subject to spin-dependent scattering is reduced, resulting inlosses of properties.

With respect to the magnetic materials, coercive force Hc, squarenessratio SQ₂ /SQ₁ and anisotropic magnetic field Hk of the magnetic thinfilms, the same conditions as previously described are useful.

For magnetic thin films satisfying these properties, preferably thefirst magnetic thin film is formed of a material containing at least 70%by weight of a composition: (Ni_(x) Fe_(1-x) (_(y) Co_(1-y) whereinletters x and y are 0.7≦x≦0.9 and 0.5≦y≦1.0 and the second magnetic thinfilm is formed of a material containing at least 70% by weight of acomposition: (Co_(z) Ni_(1-z))_(w) Fe_(1-w) wherein letters z and w are0.4≦z≦1.0 and 0.5≦w≦1.0.

The thickness t₃ of the non-magnetic thin film is preferably less than50 Å, more preferably 8 Å to 48 Å, especially 30 to 48 Å especially forreproducibility and stability of film physical properties and 35 to 48 Åfor mass production. For cost effective manufacture, t₃ may be less than30 Å, especially 10 to 28 Å. When the thickness t₃ of the non-magneticthin film is above 50 Å, there is some likelihood that the structurehave a low MR ratio and a small MR slope in a high-frequency magneticfield of 1 MHz. The non-magnetic thin film may be made of the samematerial as previously described.

In the embodiments wherein the thicknesses of the magnetic andnon-magnetic layers are controlled in the above-defined ranges, theanisotropic magnetic field Hk of the first magnetic thin film can becontrolled to 3 to 20 Oe, more preferably 3 to 16 Oe, especially 3 to 12Oe by depositing the first magnetic thin film in an external magneticfield applied in one direction in a plane coextensive with the film.Then there are obtained a high MR ratio of at least 5%, especially 6 to12%, high heat resistance, and the MR change curve has an MR slope of atleast 0.15%/Oe, more preferably at least 0.18%/Oe, especially 0.20 to0.60%/Oe in an applied magnetic field in the range between -50 Oe and+50 Oe and a maximum hysteresis width of up to 20 Oe, typically up to 16Oe, especially 0 to 14 Oe. In addition, the MR slope in a high-frequencymagnetic field of 1 MHz is at least 0.08%/Oe, more preferably at least0.10%/Oe, especially 0.10 to 0.30%/Oe. These properties insure the useof the multilayer film as reading MR heads for high density recording.If the anisotropic magnetic field Hk of the first magnetic thin film isless than 1 Oe, especially less than 3 Oe, it is approximate to thecoercive force, and the multilayer film would not provide an MR changecurve which is linear across zero magnetic field or satisfy the MR headrequirements. If the Hk is more than 20 Oe, the multilayer film wouldhave a reduced MR slope so that MR heads constructed therefrom willprovide low outputs and low resolution.

It is to be noted that the MR ratio is calculated as (ρ_(max)-ρ_(sat))/ρ_(sat) ×100% wherein ρ_(max) is maximum resistivity andρ_(sat) is minimum resistivity; the maximum hysteresis width is obtainedby measuring MR to depict an MR curve over the magnetic field rangebetween -50 Oe and +50 Oe and determining the maximum hysteresis widthfrom the hysteresis loop; the MR slope is obtained by measuring an MR todepict an MR curve, determining a differential curve thereof, anddetermining a maximum differential value over the magnetic field rangebetween -50 Oe and +50 Oe; and the high-frequency MR slope is obtainedby measuring an MR ratio in an alternating magnetic field of 5 Oe at afrequency of 1 MHz and determining a gradient thereof between -2 Oe and+2 Oe.

The artificial superlattice magnetic multilayer film of the inventionmay have any desired repetitive number (n) of alternately stackedmagnetic and non-magnetic thin films. The repetitive number (n) may besuitably selected in accordance with a desired MR ratio although n of 3or more is preferred to provide a sufficient MR ratio. As the repetitivenumber (n) is increased, the MR ratio is also increased at the sacrificeof production yield. With a too large repetitive number (n), the elementas a whole has a reduced resistance which is inconvenient for practicaluse. Then the repetitive number (n) is preferably up to 50. The longperiod superlattice structure can be observed by taking a small angleX-ray diffraction pattern where primary and secondary peakscorresponding to recurring periodicities appear.

Only two types of magnetic thin films having different coercive forcesare used in the illustrated embodiment. Another embodiment using threeor more types of magnetic thin films having different coercive forceshas the advantage that there can be provided two or more externalmagnetic fields by which the magnetization direction is reversed,expanding the range of operating magnetic field intensity.

It is also effective to alleviate the difference in surface energybetween the substrate material and the artificialsuperlattice-constituting material for improving wetting between them.In this regard, a thin film of a metal such as Cr, Fe, Co, Ni, W, Ti, V,and Mn or an alloy thereof may be formed to a thickness of about 10 to100 Å as an undercoat layer underlying the magnetic multilayer film inorder to establish a multilayer structure having a flat interface over awider area. On the surface of the uppermost magnetic thin film, ananti-oxidation film of silicon nitride or silicon oxide may be formedand a metallic conductive layer may be formed for electrode tapping.

The magnetic multilayer film can be formed by conventional methods suchas evaporation, sputtering and molecular beam epitaxy (MBE) methods. Thesubstrate may be of glass, silicon, magnesium oxide, gallium arsenide,ferrite, AlTiC and CaTiO. During deposition of the first magnetic thinfilm, an external magnetic field typically of 10 to 300 Oe is preferablyapplied on one direction in a plane coextensive with the film. Thisleads to a decrease of SQ₁ and an increase of Hk. It is to be noted thatan external magnetic field may be applied only during deposition of thefirst magnetic thin film using an apparatus including an electromagnetcapable of readily applying a magnetic field at a controlled time, butnot during deposition of the second magnetic thin film. Alternatively,an external magnetic field is applied throughout the deposition process.

Referring to FIGS. 3 and 4, the magnetic multilayer film of theinvention is shown as embodying magnetoresistance elements such as MRheads. Each of the magnetoresistance elements 10 shown in FIGS. 3 and 4includes a magnetic multilayer film 1 formed within an insulating layer5. Electrodes 3 and 3 of Cu, Ag and Au, for example, are deposited onthe magnetic multilayer film 1 for conducting measuring electric currentacross the film 1. A shunt layer 2 of Ti, for example, is joined to thelower surface of the film 1. The insulating layer 5 and hence themagnetic multilayer film 1 is sandwiched between shields 6 and 6 ofSenduct or Permalloy. In the embodiment of FIG. 4, a layer 7 ofhigh-resistivity soft magnetic material such as CoZrMo and NiFeRh isjoined to the lower surface of the shunt layer 2 for applying a biasingmagnetic field. It is to be noted that the biasing magnetic fieldapplying means and shunt layer can be omitted because the magneticmultilayer film of the invention is characterized by a better zero fieldrise.

FIG. 5 illustrates the magnetic multilayer film of the invention asbeing applied to a yoke type MR head 10. A magnetic multilayer film 1 iscovered with a thin insulating layer 5 and disposed between a pair ofyokes 8 for producing a magnetic flux. One of the yokes 8 is providedwith a notch through which the film 1 faces outward. The film 1 isprovided with electrodes (not shown) for conducting electric currentflow parallel to or perpendicular to the direction of a magnetic pathgenerated by the yokes 8. The magnetic multilayer film 1 is assembledwith a shunt layer 2 and a layer 7 for applying a biasing magnetic fieldas in FIG. 4 although the biasing magnetic field applying means andshunt layer can be omitted because the magnetic multilayer film of theinvention is characterized by a better zero field rise.

The process for the fabrication of magnetoresistance elements involvespatterning and flattening steps which include heat treatments such asbaking, annealing and resist curing. The magnetic multilayer film in thefirst preferred form of the invention is well resistant against heat andtolerates heat treatment at temperatures of up to 500° C., often 50° to400° C., typically 50° to 350° C. The magnetic multilayer films in thesecond and third preferred forms of the invention tolerate heattreatment at temperatures of up to 500° C., often 200° to 400° C. forabout one hour. Such heat treatment may be carried out in vacuum, aninert gas atmosphere or air. In the second and third preferred forms, itis preferred to carry out heat treatment in a vacuum of 10⁻⁵ to 10⁻⁹Torr because the resulting magnetic multilayer film experiences littleloss of properties.

EXAMPLE

Examples of the present invention are given below by way of illustrationand not by way of limitation.

Example 1 demonstrates the first preferred form of the invention.

EXAMPLE 1

A glass substrate (4 in FIG. 1) was placed in a ultra-high vacuumevaporation vessel which was evacuated to a vacuum of 10⁻⁹ to 10⁻¹⁰Torr. While rotating the substrate at room temperature, an artificialsuperlattice magnetic multilayer film (1 in FIG. 1) of the followingcomposition was deposited on the substrate. Deposition was carried outat a film growth rate of about 0.3 Å/sec. by an MBE method while amagnetic field was applied in one direction in a plane coextensive withthe substrate.

Table 1 shows the arrangement of magnetic and non-magnetic thin films inthe multilayer film and a magnetoresistance (MR) ratio thereof. Forexample, sample No. 3 in Table 1 is Cu(50)/Co(20)/Cu(50)/Ni₀.8 Fe₀.2(30)!x10 which means that a procedure consisting of steps ofsuccessively depositing a non-magnetic thin film of Cu of 50 Å thick, afirst magnetic thin film of NiFe or Permalloy magnetic alloy(Ni80%-Fe20%) of 30 Å thick, a second magnetic thin film of Co of 20 Åthick, and a non-magnetic thin film of Cu of 50 Å thick was repeated 10times. Since the number of repeated deposition procedures was 10 for allthe samples, each procedure or multilayer unit is expressed in Table 1as (50, 20, 30) in the order of (Cu/t₃, Co/t₂, NiFe/t₁). In all thesamples, a chromium layer of 50 Å thick was formed as an undercoatlayer.

Magnetization and a B-H loop were measured by means of a vibratingsample magnetometer (VSM). Separately for resistance measurement, thesample was cut into a strip of 0.5 mm×10 mm, which was measured forresistance by a four terminal method. For measurement, electric currentwas longitudinally passed through the strip and an external magneticfield was applied in plane and perpendicular to the electric current andvaried from -300 Oe to +300 Oe. From the resistance measurement, minimumresistivity ρ_(sat) and a MR ratio (ΔR/R) were determined. The MR ratioΔR/R is calculated according to the equation:

    ΔR/R=(ρ.sub.max -ρ.sub.sat)/ρ.sub.sat ×100%

wherein ρ_(max) is the maximum resistivity. Further, a difference in MRratio under an applied magnetic field of from -3 Oe to +3 Oe wasmeasured and regarded as a zero magnetic field gradient for evaluatingrise property. The value of zero field gradient must be 0.5% or more aspreviously mentioned.

Separately, a 2-element artificial superlattice was prepared using afirst magnetic thin film (NiFe) or a second magnetic thin film (Co) anda non-magnetic thin film (Cu). This sample was also measured forsquareness ratios SQ₁ and SQ₂, their relative ratio SQ₂ /SQ₁, andanisotropic magnetic field Hk of NiFe.

The results (initial properties) are shown in Table 1. Table 1 alsoreports the intensity of the magnetic field that was applied in onein-plane direction during NiFe deposition.

The samples were heat treated in vacuum at 350° C. for 2 hours. Table 2reports the squareness ratio, ρ_(sat), MR ratio, and zero field gradientof the heat treated samples together with their changes from the initialones.

                                      TABLE 1    __________________________________________________________________________            Multilayer film     Squareness ratio                                           Zero magnetic                                                   Magnetic                                                           First magnetic    Sample  thickness ρsat                           MR ratio                                SQ1                                   SQ2     field gradient                                                   applied during                                                           layer's HK    No.     (Cu, Co, NiFe) t2 t1                      (μΩcm)                           (%)  NiFe                                   Co SQ2/SQ1                                           (%)     deposition                                                           (Oe)    __________________________________________________________________________     1      (50, 20, 20)                      9.559                           7.7  0.19                                   0.80                                      4.2  1.3     200     3.0     2      (50, 15, 20)                      9.730                           7.4  0.21                                   0.73                                      2.9  1.2     200     6.8     3      (50, 20, 30)                      10.202                           7.9  0.11                                   0.90                                      8.2  1.9     200     5.0     4      (50, 25, 40)                      9.711                           7.1  0.12                                   0.88                                      7.3  1.8     200     4.5     5      (60, 20, 50)                      9.595                           6.6  0.11                                   0.93                                      8.5  1.8     200     5.3     6      (40, 28, 40)                      10.101                           8.1  0.15                                   0.91                                      6.1  1.4     200     7.0     7      (60, 25, 50)                      8.595                           6.5  0.17                                   0.90                                      5.3  1.8     200     6.0     8      (40, 20, 40)                      9.811                           7.8  0.14                                   0.82                                      5.9  1.2     200     8.2     9 (comparison)            (50, 10, 10)                      9.711                           5.1  0.60                                   0.55                                      0.9  1.6      0      1.2    10 (comparison)            (50, 20, 20)                      9.577                           7.7  0.88                                   0.78                                      0.9  0.6      0      0.6    11 (comparison)            (50, 40, 40)                      10.893                           5.4  0.14                                   0.91                                      6.5  0.2     200     14.3    12 (comparison)            (60, 40, 10)                      9.892                           4.6  0.60                                   0.91                                      1.5  0.4      0      0.9    13 (comparison)            (60, 20, 20)                      8.595                           6.6  0.90                                   0.62                                      0.7  0.7      0      0.5    14 (comparison)            (40, 20, 20)                      8.595                           6.6  0.97                                   0.90                                      1.1  0.2      0      0.4    15 (comparison)            (50, 30, 10)                      9.792                           5.2  0.60                                   0.91                                      1.5  0.3      0      0.7    __________________________________________________________________________

                                      TABLE 2    __________________________________________________________________________            Squareness                  After 350° C./2 hour heat treatment            ratio                Zero magnetic    Sample  SQ1               SQ2                  ρsat                       MR ratio  field gradient    No.     NiFe               Co (μΩcm)                       (%)                          Change (%)                                 (%)                                    Change (%)    __________________________________________________________________________     1      0.21               0.82                  10.121                       5.8                          -25    1.7                                     +6     2      0.23               0.78                  10.366                       5.3                          -28    1.1                                     -8     3      0.13               0.88                  10.894                       6.1                          -23    2.2                                    +16     4      0.15               0.88                  10.412                       5.5                          -23    1.6                                     -9     5      0.14               0.90                  10.023                       5.2                          -21    2.1                                    +14     6      0.16               0.89                  10.988                       5.9                          -27    1.7                                    +21     7      0.17               0.87                  9.874                       5.1                          -22    1.6                                    -11     8      0.16               0.85                  10.294                       6.2                          -21    1.5                                    +25     9 (comparison)            0.62               0.56                  10.396                       2.6                          -49    0.08                                    -95    10 (comparison)            0.84               0.69                  11.114                       4.3                          -44    0.21                                    -62    11 (comparison)            0.92               0.93                  11.738                       4.1                          -24    0.18                                    -10    12 (comparison)            0.58               0.92                  10.912                       3.1                          -33    0.23                                    -43    13 (comparison)            0.82               0.65                  9.371                       3.2                          -52    0.31                                    -58    14 (comparison)            0.87               0.86                  9.426                       3.3                          -50    0.16                                    -30    15 (comparison)            0.61               0.93                  10.761                       2.1                          -68    0.11                                    -95    __________________________________________________________________________

As is evident from the date of Table 2, only sample Nos. 1 to 8 withinthe scope of the invention provide a zero field gradient of more than 1%and an MR ratio of more than 5% both at the initial and after the heattreatment.

FIG. 6 shows M-H loops of as-deposited first and second magnetic thinfilms constituting sample No. 3. FIG. 7 shows the zero magnetic fieldgradient versus Hk of the first magnetic thin film. FIGS. 8 and 9 areX-ray diffraction patterns of as-deposited and heat treated sample No.3, respectively. It is seen from these figures that the samples withinthe scope of the invention maintain a artificial periodicity latticestructure both as deposited and after heat treatment.

Example 2 demonstrates the second preferred form of the invention.

EXAMPLE 2

A three-element artificial lattice magnetic multilayer film Cr(50)Cu(50)--Co(10)--Cu(50)--NiFe(10)!x10 was formed on a glass substrate ina MBE apparatus using a ultra-high vacuum multi-source evaporationtechnique. The ultimate vacuum was 4×10⁻¹¹ Torr, the vacuum duringdeposition was 8×10⁻¹⁰ Torr, and the film growth rate was 0.2 to 0.5Å/sec. A magnetic field of 180 Oe was applied in an in-plane directionduring deposition.

An MR curve of the resulting sample was measured. FIG. 10 is a chartobtained by sweeping 5 cycles the intensity of applied magnetic fieldover the range between -10 Oe and +10 Oe. The MR curve showed a MR slopeof 0.30%/Oe and a MR ratio of 5.7%, and included a linear portion over amagnetic field width of about 8 Oe.

The third preferred form of the invention is demonstrated by Examples3-6 and Comparative Example 1.

EXAMPLE 3

An artificial lattice was prepared by depositing a non-magnetic metallayer of Cr on a Corning 7059 glass substrate to form an undercoat layerof 50 Å and then depositing a magnetic multilayer film of Cu/Co/Cu/NiFewith a number of repetitive deposition procedures of 10. Deposition by aMBE technique was carried out under conditions including an ultimatevacuum of 2×10⁻¹⁰ Torr, a vacuum during deposition of 1×10⁻⁹ Torr, asubstrate temperature of about 40° C., and a film growth rate of 0.1 to0.4 Å/sec. A magnetic field of 180 Oe was applied in an in-planedirection of the substrate during deposition.

Sample Nos. 21 to 27 were prepared in the magnetic field of 90 Oe bydepositing magnetic multilayer films while varying the thicknesses ofrespective layers (Cu/t₃, Co/t₂, NiFe/t₁) as shown in Table 3, and thenheat treating in vacuum at 250° C. for one hour. The samples wereevaluated with the results shown in Table 3. Film thickness is expressedin angstrom (Å). It is to be noted that samples Nos. 21 to 27 had a SQ₁of 0.01 to 0.5, a SQ₂ of 0.7 to 1.0, and a SQ₂ /SQ₁ ratio between 2 and100.

                                      TABLE 3    __________________________________________________________________________            Multilayer film   First magnetic    Sample  thickness                    ρsat                         MR ratio                              layer's HK                                      MR slope                                            High-frequency slope    No.     (t3, t2, t1)                    (μΩcm)                         (%)  (Oe)    (%/Oe)                                            at 1 MHz, %/Oe)    __________________________________________________________________________    21      (42, 10, 13)                    9.848                         8.1  7.1     0.25  0.12    22      (43, 10, 10)                    10.058                         8.4  8.2     0.21  0.13    23      (41, 13, 15)                    10.118                         7.6  6.5     0.22  0.11    24      (45, 12, 18)                    9.819                         7.8  5.3     0.27  0.16    25      (12, 12, 15)                    15.382                         6.5  6.3     0.90  0.10    26 (comparison)            (50, 10, 10)                    9.316                         5.7  8.0     0.30  0.06    27 (comparison)            (60, 10, 10)                    9.012                         5.7  7.6     0.19  0.06    31 (comparison)            (45, 10, 13)                    9.051                         7.0  0.8     0.23  0.06    32 (comparison)            (45, 10, 10)                    8.915                         6.1  1.1     0.16  0.02    33 (comparison)            (42, 13, 13)                    10.276                         7.9  0.8     0.22  0.07    34 (comparison)            (50, 10, 10)                    9.238                         5.6  1.2     0.29  0.07    35 (comparison)            (55, 10, 10)                    9.124                         4.2  1.2     0.18  0.05    __________________________________________________________________________

COMPARATIVE EXAMPLE 1

Sample Nos. 31 to 35 were prepared by depositing magnetic multilayerfilms by the same procedure as Example 3 except that no magnetic fieldwas applied.

The thicknesses of respective layers (Cu/t₃, Co/t₂, NiFe/t₁) were variedas shown in Table 3. The films were heat treated as in Example 3. Thesamples were evaluated with the results shown in Table 3. Film thicknessis expressed in angstrom (Å). It is to be noted that sample Nos. 31 to35 had a SQ₁ in excess of 0.5.

As seen from Table 3, a large high-frequency slope was obtained when thefirst magnetic thin film was deposited in the presence of an appliedmagnetic field so as to provide an anisotropic magnetic field Hk of 3 to20 Oe. Even when Hk was in the desirable range, a gentle high-frequencyslope was obtained at t₃ ≧50 Å.

EXAMPLE 4

Magnetic multilayer films were prepared by the same procedure as inExample 3 except that both the Co and NiFe layers had a fixed thicknessof 10 Å and the thickness of Cu layers was varied to 35, 42, 45 and 50Å. A magnetic field of 180 Oe was applied during deposition. The filmswere measured for MR ratio, with the results shown in FIG. 11.

MR ratio was improved when the thickness of Cu layers was less than 50 Å(t₃ <50 Å). Additionally, MR ratio was significantly increased ascompared the MR ratio that would be achieved when no Hk was imparted tothe NiFe layers.

EXAMPLE 5

Magnetic multilayer films were prepared by the same procedure as inExample 3 except that the Co layers had a fixed thickness of 10 Å, theCu layers had a fixed thickness of 45 Å and the thickness of NiFe layerswas varied to 10, 13, 15, 20, 30, 40 and 50 Å. A magnetic field of 180Oe was applied during deposition. MR curves of the films were determinedover a magnetic field range between -50 Oe and +50 Oe, from which themaximum hysteresis width which is the width of opening of a MR curve wasobtained.

The results are shown in FIG. 12. It is seen that the maximum hysteresiswidth of a MR curve increases as the NiFe layers are increased inthickness.

EXAMPLE 6

A magnetic multilayer film of Cr(50)Cu(42)--Co(10)--Cu(42)--NiFe(13)!×10 was deposited by the same procedureas in Example 3 except that the magnetic field applied during depositionhad an intensity of 90 Oe.

An MR curve of the resulting sample was measured. FIG. 13 is a chartobtained by sweeping 5 cycles the intensity of applied magnetic fieldover the range between -50 Oe and +50 Oe. Little hysteresis wasacknowledged on the MR curves.

EXAMPLE 7

Two magnetic multilayer films of Cr(50 )Cu(42)--Co(10)--Cu(42)--NiFe(13)!x10 were deposited by the sameprocedure as in Example 3 while deposition was done in the presence orabsence of a magnetic field of 180 Oe. They are designated amagnetic-field-applied sample and a magnetic-field-free sample. For boththe samples, a strip of 0.5×6 mm (for the MR properties estimation) anda disk of 10 mm (for the structural estimation) diameter were patternedfrom the same substrate. The magnetic-field-applied samples were heattreated at temperatures of 150°, 200°, 250°, 300° and 400° C., and themagnetic-field-free samples were heat treated at temperatures of 200°,250° and 300° C., all in vacuum for one hour. The samples both asdeposited and after heat treatment were determined for MR ratio and MRslope. The results of MR slope were shown in FIG. 14. The values ofas-deposited samples are plotted at a heat treatment temperature of 50°C.

In the magnetic-field-applied samples, the MR slope remained unchangedafter heat treatment. In the magnetic-field-free samples, the MR slopesignificantly decreased after heat treatment. The same results wereobtained for MR ratio.

FIG. 15 shows small-angle X-ray diffraction patterns of themagnetic-field-applied samples after heat treatment at differenttemperatures. There is found little difference in the position andintensity of a diffraction peak corresponding to the artificial latticeperiodicity, indicating the retention of the structure.

The first preferred form of the invention provides a magnetic multilayerfilm having a great MR ratio of several percents to several ten percentsin a low external magnetic field of several oersted to several tenoersted, a sharp rise at zero magnetic field and high heat resistance.The second preferred form of the invention provides a magneticmultilayer film additionally having improved hysteresis and MR slope inan applied magnetic field in the range between -10 Oe and +10 Oe. Thethird preferred form of the invention provides a magnetic multilayerfilm having a high MR slope of at least 0.15%/Oe in an applied magneticfield in the range between -50 Oe and +50 Oe, improved hysteresis of MRratio, and a high MR slope in a high-frequency magnetic field. Fromthese magnetic multilayer films, there are obtained improved MR elementsas typified by high sensitivity MR sensors and MR heads capable of highdensity magnetic recording.

We claim:
 1. A magnetic multilayer film, comprising a first and a secondmagnetic thin film with a non-magnetic thin film between said first andsecond magnetic thin films, whereinsaid first and second magnetic thinfilms have different coercive forces, said first magnetic thin filmhaving a lower coercive force and a squareness ratio SQ₁ of from 0.01 to0.05, and said second magnetic thin film having a higher coercive forceand a squareness ratio SQ₂ of from 0.7 to 1.0, said first magnetic thinfilm has a thickness t₁, said second magnetic thin film has a thicknesst₂, and 4Å≦t₂ <30Å, 6Å≦t₁, and t₁ ≧t₂.
 2. The magnetic multilayer filmof claim 1 wherein SQ₂ /SQ₁ is from 2 to
 100. 3. The magnetic multilayerfilm of claim 1 wherein said first magnetic thin film has an anisotropicmagnetic field Hk of 1 to 20 Oe.
 4. The magnetic multilayer film ofclaim 3 wherein said first magnetic thin film has an anisotropicmagnetic field Hk of 3 to 20 Oe.
 5. The magnetic multilayer film ofclaim 1 wherein said non-magnetic thin film has a thickness t₃ whereint₃ <50 Å.
 6. The magnetic multilayer film of claim 1 wherein 20 Å≦t₁. 7.The magnetic multilayer film of claim 6 wherein 4 Å≦t₂ ≦28 Å, 22 Å≦t₁,and t₁ ≧1.05t₂.
 8. The magnetic multilayer film of claim 1 wherein 4Å≦t₂ <20 Å, 10 Å≦t₁ <20 Å, and t₁ ≧t₂.
 9. The magnetic multilayer filmof claim 1 wherein 4 Å≦t₂ <30 Å, 6 Å≦t₁ ≦40 Å, and t₁ ≧t₂.
 10. Themagnetic multilayer film of claim 9 wherein said non-magnetic thin filmhas a thickness t₃ wherein t₃ <50 Å.
 11. The magnetic multilayer film ofclaim 1 which produces a magnetoresistance curve which includes a linearportion having a slope of at least 0.15%/Oe in the magnetic field rangebetween -50 Oe and +50 Oe and has a maximum hysteresis width of up to 20Oe.
 12. A magnetic multilayer film, comprising a first and a secondmagnetic thin film with a non-magnetic thin film between said first andsecond magnetic thin films, whereinsaid first and second magnetic thinfilms have different coercive forces, said first magnetic thin filmhaving a lower coercive force and a squareness ratio SQ₁ of from 0.01 to0.5, and said second magnetic thin film having a higher coercive forceand a squareness ratio SQ₂ of from 0.7 to 1.0, said first magnetic thinfilm has a thickness t₁, said second magnetic thin film has a thicknesst₂, and 4Å≦t₂ <30Å, 6Å≦t₁, and t₁ ≧t₂, wherein said first magnetic thinfilm comprises (Ni_(x) Fe_(1-x))_(y) Co_(1-y) wherein 0.7≦x≦0.9 and0.5≦y≦1.0.
 13. A magnetic multilayer film, comprising a first and asecond magnetic thin film with a non-magnetic thin film between saidfirst and second magnetic thin films, whereinsaid first and secondmagnetic thin films have different coercive forces, said first magneticthin film having a lower coercive force and a squareness ratio SQ₁ offrom 0.01 to 0.5, and said second magnetic thin film having a highercoercive force and a squareness ratio SQ₂ of from 0.7 to 1.0, said firstmagnetic thin film has a thickness t₁, said second magnetic thin filmhas a thickness t₂, and 4Å≦t₂ <30Å, 6Å≦t₁, and t₁ ≧t₂, wherein saidsecond magnetic thin film comprises (Co_(z) Ni_(1-z))_(w) Fe_(1-w)wherein 0.4≦z≦1.0 and 0.5≦w≦1.0.
 14. The magnetic multilayer film ofclaim 1 wherein said first magnetic thin film has been deposited whileapplying an external magnetic field in one in-plane direction.
 15. Themagnetic multilayer film of claim 14 wherein said external magneticfield has an intensity of 10 to 300 Oe.
 16. The magnetic multilayer filmof claim 1 which is prepared by a method comprising the stepsof:depositing at least said first and second magnetic thin films whileinterposing a non-magnetic thin film therebetween and effecting heattreatment at a temperature of up to 500° C.
 17. A magnetoresistanceelement, comprisinga substrate; and a magnetic multilayer film,comprising a first and a second magnetic thin film with a non-magneticthin film between said first and second magnetic thin films, whereinsaid first and second magnetic thin films have different coerciveforces, said first magnetic thin film having a lower coercive force anda squareness ratio SQ₁ of from 0.01 to 0.5, and said second magneticthin film having a higher coercive force and a squareness ratio SQ₂ offrom 0.7 to 1.0, said first magnetic thin film has a thickness t₁, saidsecond magnetic thin film has a thickness t₂, and 4Å≦t₂ <30Å, 6Å≦t₁, andt₁ ≧t₂.
 18. The magnetoresistance element of claim 17, wherein SQ₂ /SQ₁is from 2 to
 100. 19. The magnetoresistance element of claim 17, whereinsaid first magnetic thin film has an anisotropic magnetic field Hk of 1to 20 Oe.
 20. The magnetoresistance element of claim 19, wherein saidfirst magnetic thin film has an anisotropic magnetic field Hk of 3 to 20Oe.
 21. The magnetoresistance element of claim 17, wherein saidnon-magnetic thin film has a thickness t₃ wherein t₃ <50 Å.
 22. Themagnetoresistance element of claim 17, wherein 20 Å≦t₁.
 23. The magneticmultilayer film of claim 22, wherein 4 Å≦t₂ ≦28 Å, 22 Å≦t₁, and t₁≧1.05t₂.
 24. The magnetic multilayer film of claim 17, wherein 4 Å≦t₂<20 Å, 10 Å≦t₁ <20 Å, and t₁ ≧t₂.
 25. The magnetic multilayer film ofclaim 17, wherein 4 Å≦t₂ <30 Å, 6 Å≦t₁ ≦40 Å, and t₁ ≧t₂.
 26. Themagnetoresistance element of claim 25, wherein said non-magnetic thinfilm has a thickness t₃ wherein t₃ <50 Å.
 27. The magnetoresistanceelement of claim 17, which produces a magnetoresistance curve whichincludes a linear portion having a slope of at least 0.15%/Oe in themagnetic field range between -50 Oe and +50 Oe and has a maximumhysteresis width of up to 20 Oe.
 28. A magnetoresistance element,comprisinga substrate; and a magnetic multilayer film, comprising afirst and a second magnetic thin film with a non-magnetic thin filmbetween said first and second magnetic thin films, wherein said firstand second magnetic thin films have different coercive forces, saidfirst magnetic thin film having a lower coercive force and a squarenessratio SQ₁ of from 0.01 to 0.05, and said second magnetic thin filmhaving a higher coercive force and a ssquareness ratio SQ₂ of from 0.7to 1.0, said first magnetic thin film has a thickness t₁, said secondmagnetic thin film has a thickness t₂, and 4Å≦t₂ <30Å, 6Å≦t₁, and t₁≧t₂, wherein said first magnetic thin film comprises (Ni_(x)Fe_(1-x))_(y) Co_(1-y) wherein 0.7≦x≦0.9 and 0.5≦y≦1.0.
 29. Amagnetoresistance element, comprisinga substrate; and a magneticmultilayer film, comprising a first and a second magnetic thin film witha non-magnetic thin film between said first and second magnetic thinfilms, wherein said first and second magnetic thin films have differentcoercive forces, said first magnetic thin film having a lower coerciveforce and a squareness ratio SQ₁ of from 0.01 to 0.5, and said secondmagnetic thin film having a higher coercive force and a squareness ratioSQ₂ of from 0.7 to 1.0, said first magnetic thin film has a thicknesst₁, said second magnetic thin film has a thickness t₂, and 4Å≦t₂ <30Å,6Å≦t₁, and t₁ ≧t₂, wherein said second magnetic thin film comprises(CO_(z) Ni_(1-z))_(w) Fe_(1-w) wherein 0.4≦z≦1.0 and 0.5≦w≦1.0.
 30. Themagnetoresistance element of claim 17, wherein said first magnetic thinfilm has been deposited while applying an external magnetic field in onein-plane direction.
 31. The magnetoresistance element of claim 30,wherein said external magnetic field has an intensity of 10 to 300 Oe.32. The magnetoresistance element of claim 17 which is prepared by amethod comprising the steps of:depositing at least two magnetic thinfilms while interposing a non-magnetic thin film therebetween andeffecting heat treatment at a temperature of up to 500° C.
 33. Themagnetoresistance element of any one of claims 16-28, wherein saidmagnetoresistance element does not have means for applying a biasingmagnetic field.